1. Field of the Invention
This invention relates to a dielectric ceramic composition and, more particularly, an improved dielectric ceramic composition with a high dielectric constant of not less than 8000 and a low sintering temperature of 900.degree. to 1000.degree. C.
2. Description of the Prior Art
Recently, electronic appliances for industrial and consumer uses are required to have a design so that they are small, light-weight and functions at high frequencies. For this reason, there is an increasing demand for monolithic ceramic capacitors because of their large capacitance-to-volume ratio, high mass producibility and excellent electrical and physical characteristics including high frequency characteristics and heat resistance.
The monolithic ceramic capacitors are generally built up of an arrangement of alternating two layers of a dielectric layer, composed of a dielectric ceramic composition of a barium titanate system, and an internal electrode. The dielectric ceramic composition of the prior art has a high sintering temperature of 1300.degree. to 1400.degree. C., so that it has been required to use a noble metal such as Au, Pt and Pd as a material for internal electrodes. However, the noble metals are expensive to use and occupies the greater part of the manufacturing cost of the monolithic ceramic capacitors. Thus, the use of the noble metal sets a limit to lower the manufacturing cost of the monolithic ceramic capacitors.
To solve this problem, it has been proposed to incorporate a glass component comprising oxides of boron, bismuth and lead into the above modified barium titanate composition. The addition of the glass component lowers the sintering temperature to 1100.degree. to 1150.degree. C., thus making it possible to use a relatively inexpensive silver-paradium alloy as a material for internal electrodes. However, the incorporation of the glass component causes lowering of the dielectric constant, and thus the monolithic ceramic capacitors increase in size for a given capacitance. This results in increase in an amount of the electrode material to be used, thus making it difficult to reduce the manufacturing cost of the monolithic ceramic capacitors.
It is an object of the present invention to provide a dielectric ceramic composition with a high dielectric constant of not less than 8000 and a low sintering temperature of 900.degree. to 1000.degree. C.
Another object of the present invention is to provide a dielectric ceramic composition capable of being used as a dielectric material for monolithic ceramic capacitors comprising internal electrodes of a relatively inexpensive silver-paradium alloy.